Byblical connections

So, we have Gods(Ankhseram, Chronos and some other), now we have Angels (Black, White and Scarlet). It's most likely taken from the Bible. Also, the future chapter called "The Third Seal" most likely refers to "Third Seal", one of the seven in the "A scroll, with seven seals" in the "Book of Revelation" in the Bible. Also Acnologia is "The Black Dragon in the Book of Apocalypse" and "Book of Apocalypse" could refer to "Book of Revelation" also known as "Revelation or The Apocalypse of John" in the Bible. And also we have demons. Acnologia could refer to horseman riding a black horse in the "Book of Revelation". And coincidence or not this horseman is related to a "third seal" written in the Bible. More on this

Bible and black horse

Angels

Who are the so called Angels for now it is a mistery. I believe they are new race of beings. So we have Gods, Demons, Dragons and now Angels. We could assume, they are very powerful. In the legend taled by Eileen they have clashed and White angel won, this is the reason why mountain Zonia is covered in snow, the clash could have caused this. Also, we now know(most likely) Eileen, who is an Angel has the power most likely equal to August's. That's really something.

Eileen(Irene)

She is an angel. I assume that from translations I read. Now we can guess who she is in the siluettes of 12 Spriggans, well, obviously, the one with the wings. Here she is:

Eileen silhouette

Only difference in appearance we see now is that her hair is straigth and in recent chapter she has it braided. In Bible it is described how Angel defeated dragon. Again, Bible:

"Then I saw an angel coming down from heaven, holding in his hand the key to the bottomless pit and a great chain. And he seized the dragon, that ancient serpent, who is the devil and Satan, and bound him for a thousand years, and threw him into the pit, and shut it and sealed it over him, so that he might not deceive the nations any longer".

Also, Zeref touching ground and talking about change of quality of the magic inside the earth adds to my theory.

Acnologia

In spoilers for chapter 486 I see two possible translations of Eileen's words about Acnologia:

"The Black Dragon is the Black Angel's Grudge"

and

"The Black Dragon is LIKE the Black Angel's Grudge".

Judging from each translation there are two possiblities:

1. If the word LIKE is present, then Acnologia likely has no relationship to angels. Just passer by.

1. But if the word LIKE is ommited, then context changes a lot. It means, that Acnologia has some direct connections to Angels. He was present at White and Black angel clash or became a result of this clash. So to sum up everything we know, Angels, Dragons (dragon civil war) and Acnologia are somehow connected. In Dragon Civil War two fractions existed, the one, which consisted anti-human dragons, and other which supported humans. Acnologia must had started in the one, which supported humans, because he was tought dragon slayer magic. So how Acnologia started to hate dragons? Addition of Angels to the story may give us an answer.

Example, both White and Black angels fell in love with Acnologia, but Acnologia only loved the Black one. And the White one with the help of the dragons had killed the Black one. Acnologia got mad, and killed all the dragons despite being tought by them. Maybe he also killed the White angel in process. So this is why he is called "the Black Angel's Grudge", or maybe in other words black angel's anger.

The truth remains to be seen.